1. Technical Field of the Invention
The present invention relates generally to wind tunnels and more particularly to a nozzle diffuser for use with the open test section of wind tunnels.
2. Discussion of the Related Art
A conventional wind tunnel operating with an open test section comprises a contracted tunnel section for supplying the air or other gas jet stream to the inlet end of the open test section. The contracted section, frequently called the contraction, is designed for accelerating the gas or air before it enters the open test section. After traversing the length of the open test section, the flow is then directed toward a diffuser located at the exit end of the open test section. The purpose of the diffuser is to decelerate the flow and thereby increase its pressure by a process called recovery.
The flow exiting from the contraction has a desired uniform profile and the resulting jet usually has a rectangular or oval shape. As the flow traverses the open test section it tends to develop an outer shear layer which ultimately leads to non-uniformity involving a mixing process. While the outer layer mixes with the surroundings, the uniform portion of the jet, called the jet core, diminishes in size. By the time the flow enters the diffuser the flow is usually far from being uniform which causes a loss in the pressure recovery, necessitating increased energy, e.g., fan power being needed to keep the flow moving.
One proposed correction of this non-uniformity is to use tabs or other similar devices located at the perimeter of the contraction exit in an effort to break up and weaken the shear layer surrounding the emerging jet stream. However, these tabs also tend to reduce the effective size of the jet core, which is often undesirable.